The Immunological Monitoring Core B is a very essential component of the SCCOR grant. This core will assist all four scientific projects and will provide the necessary information to the other cores. The Specific Aims of this core are: Aim 1: To procure, triage and store peripheral blood mononuclear cells, plasma and serum, and endomyocardial biopsy tissue specimens. Aim 2: To process the specimens as required by individual investigators for experimental protocols in the clinical and basic projects. Aim 3: To establish the human lymphoblastoid cell lines (LCL) from peripheral blood for each patient, and maintain the cell lines for EBV in vitro studies. Aim 4: To develop, evaluate and perform in vitro monitoring assays to determine the frequency and activity of immune effector cells in order to support basic and clinical projects. The core will make available to the investigators the specimens obtained from pediatric heart and heart-lung transplant recipients participating in the various studies. In order to assess the immune modulation effect of biotherapies and/or impact of elevation of EBV load, these serial specimens will be tested in a panel of assays developed and validated by the Core. These assays will identify, quantitate and characterize the allo-reactive T-cells in the circulation. Other assays will measure and characterize the immune defects of EBV-specific T cells in peripheral blood of these patients. The development of such assays and their application to assess of immune functions in the course of therapy are essential components of the Core. The Core will also perform HLA DNA typing required for projects 1-3.